Jun 6th 2015 |

Observing Tips

Below are some basic techniques that experienced observers use all the time to enhance their viewing. Many beginners are disappointed that they cannot see some of the details described in books or by other advanced observers. All that is needed is to use the right methods of observing to see much more. Employ these little tricks to get the most out of your stargazing.

Use Averted Vision

This technique alone will allow you to see easily twice as much detail when stargazing. The human eye contains two sets of light-sensitive cells: the cones which see color and the rods which see black and white. While sensitive to color, the cones are very insensitive at low light levels. (This is why you don’t see color in faint objects through a telescope, but bright objects like planets still show color.) The rods take over at night because they have greater dim-light sensitivity. But the cones are located in the center of the eye, and the rods are mostly located around the periphery. This means looking directly at a celestial object uses the insensitive cones, but looking off to the side of the object puts the light from the object right onto the rods. New observers are surprised how much detail pops out when using averted vision. Objects otherwise invisible suddenly are seen, and faint details like spiral arms in a galaxy or faint stars around the edge of a globular cluster become visible. Once you start using averted vision it will become perfectly natural and you will begin doing it without even thinking about it.

Get Dark Adapted

Not only is it important to have dark skies for observing, it is critical to be dark adapted. If you’ve ever gone for a hike under the full moon you know how much it is possible to see with faint light. The moon gives off a half million times less light than the sun, showing that the human eye has a huge dynamic range, allowing you to see in all conditions. But the change from seeing in bright light to dim light does not happen instantly. In addition to rapid changes like the pupils opening up, chemical changes begin to occur allowing you to see at lower light levels. These chemical changes take from fifteen to thirty minutes to take full effect. After walking outside to observe or after using a flashlight for setting up the telescope, give yourself some time to adjust to the dark before expecting the best views. Also, take care to preserve your night vision once you are adapted so you don’t have to start over again. Use a red flashlight for reading star charts. The human eye is least sensitive to red light so this type of flashlight will not be as likely to ruin your dark adaptation.

Eliminate Stray Light

This might seem obvious, but local light sources like your neighbor’s motion sensor lights going off every time his dog goes out can ruin your night vision. As well, bright nearby lights can shine into the telescope and reflect off optical surfaces to reduce contrast. When setting up the telescope, consider where light sources will be and try to block them as best as possible by setting up where a wall or fence will be between your scope and the light source. A dew shield works well to keep light out of the telescope tube. Inviting neighbors over to view through the scope usually works well for getting them to turn off lights at night. Diplomacy always works better than firing a slingshot at their light bulbs. Some observers go as far as setting up panels to block stray light sources. Of course, the best solution is to drive out away from the city entirely, but on nights when you have to stay home to observe, do what you can to keep stray light under control.

Eliminate Vibration

A shaky telescope can ruin an otherwise good observing session. The obvious place to start stabilizing a telescope is its tripod. A good telescope should already have a pretty stout tripod, but occasionally scopes are under-mounted. If this is the case, a great solution are Vibration Suppression Pads, such as those made by Celestron. These pads are about the size of hockey pucks and contain a material known as Sorbothane. Originally used to dampen vibration in turntables, Sorbothane has an almost magical ability to reduce vibration in telescopes. The pads are placed under the tripod legs and shaking is reduced significantly. Vibration reduction pads have to be seen to be believed. If vibration is an issue, this is a great solution.

In addition to minimizing existing vibration, try to avoid setting up the telescope in a place that might induce vibration. A popular place to set up a telescope is on a flat rooftop, but this is a notoriously unstable position. Since rooftop areas are often not supported in the center, they have a tendency to flex as someone walks around. If you are observing alone, this might not be a problem, but when sharing the view, expect some shakiness as people move about. While a rooftop location may get you away from trees and other houses, unless there is no other option try to avoid setting up there. See the next section for another reason rooftops are less than ideal observing locations. Similar to a rooftop, wooden decks are often unstable. Your best bet is to set up on stable, solid ground whenever you can.

Minimize Turbulence

The steadiness of the atmosphere–known as seeing conditions–is critically important to observation, especially of the planets. While there is little you can do to control inherent atmospheric turbulence caused by wind or cold fronts or the jet stream, you can try to avoid local conditions that give rise to choppy air. In the wintertime, houses and other building often vent warm air which causes turbulence. Try to avoid looking low over buildings, especially around chimneys or vents. Likewise, dark rooftops hold in heat during the day and release it again after dark. This is another reason not to setup on a flat rooftop, as the heat radiating off it can distort the views through the telescope. Cold air pools into low-lying areas, often causing turbulence. Streams and desert washes tend to produce poor seeing conditions in cold months for this reason. One of the worst places to be in cold weather is at the bottom of a mountain range. Cold air will sink down the faces of the peaks and roll across the valley or pool into basins, producing awful seeing. This is one of many reasons observatories are built at the tops of mountains. But even mountains themselves generate bad seeing sometimes, as they chop up airflow. Isolated peaks tend to have better seeing than peaks in the middle of larger ranges. These are all things to consider when selecting an observing sight, especially for high-resolution viewing or imaging.

Use the Correct Magnification

There are two common magnification myths in astronomy. The first is that more magnification is better. The assumption of many beginners is that to see things farther away you need more power. But the trick isn’t seeing farther, it’s seeing fainter. And for this, aperture is the key more than magnification. In fact, lower power produces a brighter image and almost always produces a better view than high power. However, this leads to the second myth, an assumption made by more experienced stargazers: that lower power is always better. The truth is, there is an ideal magnification depending on the telescope used, the object being viewed, and the observer’s visual acuity. In general, a medium magnification produces the best view.

Low power is great for finding objects and for viewing very large objects such as the Pleiades or Andromeda Galaxy. High magnification can be good for small targets like planets or double stars, but most observers quickly learn that there is definitely such a thing as too much magnification. For most deep-sky objects, though, medium power is ideal for bringing out the most detail. We’ll spare you the details here, but suffice to say that it has to do primarily with the resolving power of the human eye. (See the Observing Theory page for all the gory details.) In general, use the following guidelines for magnification.

Lowest Power

4x per inch of aperture

Best Resolution

12x per inch of aperture

Highest Power

30x per inch of aperture

For example, using an 8″ telescope, the minimum magnification would be around 32x, the best resolution for deep sky objects would occur at around 96x, and the highest useable magnification would be around 240x.

Use the Right Filters

Filters can be used to bring out a great amount of detail when used properly. By far the best filter to have is a polarizing filter. A polarizing filter works by cutting down the amount of light coming through the telescope and is adjustable to vary the amount of light transmission. Nothing works better on the moon and planets to enhance detail. The moon in particular can be so bright that it is difficult to look at, especially with a larger telescope. Planetary detail is subtle and can easily be lost in the glare of a bright planet like Jupiter or Mars. Using a filter to cut down on the brightness of the planet will allow much more detail to show through.

The next best filter to use is a narrowband nebula filter. Nebula filters work by blocking out light pollution but transmitting the light given off bynebulae. They only work on nebulas and not galaxies or clusters, but they are worth their weight in gold for improving detail. These filters work best when the observer is dark adapted, so be sure to give yourself ample time to adjust to the darkness before using one.

Take Your Time

This technique probably cannot be overstated. Remember, what we’re doing with telescopes is called observation for a reason. Take your time and really observe an object. Spending even 2-3 minutes studying a field of view will reveal vastly more detail than simply glancing at an object then hurrying on to the next. Stephen James O’Meara has written great observing guides to the Messier objects and Caldwell objects, and his drawings of these celestial subjects show a wealth of detail. People often are amazed at how much detail O’Meara can see with a small telescope. While he might be gifted with unusual visual acuity, what really makes him a world class observer is the fact that he really takes time to study the objects. Says O’Meara is his first guide: “For most of the Messier objects, I observed each for an average of six or more hours over three nights. Some of the more complex objects were observed for three hours per night for several nights. Don’t expect to see all the detail in my drawings with just a glance. Challenge yourself to spend the time to really study these objects… .” A quick glance at Saturn shows it rings; a long look reveals divisions in the rings, cloud bands, subtle colorations, and moons. No technique on this list will show you more than spending time examining an object in detail.

Have a Seat

This trick goes hand in hand with taking your time observing. You will see more if you sit while viewing. For one, this allows you more time to relax and examine the field of view. Your body is not concentrating on balancing in the dark and the muscle strain of standing up and bending over. Relaxing while viewing lets you mind concentrate more on the view. There is also a tendency to move around a bit while standing and observing, so sitting helps to stabilize the view. There’s no sense in setting up a rock-solid tripod on stable ground just to have your body wobble about in the dark and blur the image in the eyepiece. Take the strain off your body so your brain can fully enjoy the wonders of the heavens.